# std::ranges::max_element

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< cpp‎ | algorithm‎ | ranges

Defined in header `<algorithm>` |  |
Call signature |  |
template< std::forward_iterator I, std::sentinel_for<I> S, class Proj = std::identity, std::indirect_strict_weak_order<std::projected<I, Proj>> Comp = ranges::less > constexpr I max_element( I first, S last, Comp comp = {}, Proj proj = {} ); | (1) | (since C++20)
template< ranges::forward_range R, class Proj = std::identity, std::indirect_strict_weak_order< std::projected<ranges::iterator_t<R>, Proj>> Comp = ranges::less > constexpr ranges::borrowed_iterator_t<R> max_element( R&& r, Comp comp = {}, Proj proj = {} ); | (2) | (since C++20)

1) Finds the greatest element in the range `[`first`,` last`)`.
2) Same as (1), but uses r as the source range, as if using ranges::begin(r) as first and ranges::end(r) as last.

The function-like entities described on this page are algorithm function objects (informally known as niebloids), that is:

- Explicit template argument lists cannot be specified when calling any of them.
- None of them are visible to argument-dependent lookup.
- When any of them are found by normal unqualified lookup as the name to the left of the function-call operator, argument-dependent lookup is inhibited.

### Parameters

first, last | - | iterator-sentinel pair denoting the range to examine
r | - | the range to examine
comp | - | comparison to apply to the projected elements
proj | - | projection to apply to the elements

### Return value

Iterator to the greatest element in the range `[`first`,` last`)`. If several elements in the range are equivalent to the greatest element, returns the iterator to the first such element. Returns last if the range is empty (i.e. if first == last).

### Complexity

Exactly max(N - 1, 0) comparisons, where N = ranges::distance(first, last).

### Possible implementation

    struct max_element_fn
    {
        template<std::forward_iterator I, std::sentinel_for<I> S, class Proj = std::identity,
                 std::indirect_strict_weak_order<std::projected<I, Proj>> Comp = ranges::less>
        constexpr I operator()(I first, S last, Comp comp = {}, Proj proj = {}) const
        {
            if (first == last)
                return last;

            auto largest = first;
            while (++first != last)
                if (std::invoke(comp, std::invoke(proj, *largest), std::invoke(proj, *first)))
                    largest = first;
            return largest;
        }

        template<ranges::forward_range R, class Proj = std::identity,
                 std::indirect_strict_weak_order<
                     std::projected<ranges::iterator_t<R>, Proj>> Comp = ranges::less>
        constexpr ranges::borrowed_iterator_t<R>
            operator()(R&& r, Comp comp = {}, Proj proj = {}) const
        {
            return (*this)(ranges::begin(r), ranges::end(r), std::ref(comp), std::ref(proj));
        }
    };

    inline constexpr max_element_fn max_element;

### Example

Run this code

    #include <algorithm>
    #include <cmath>
    #include <iostream>

    int main()
    {
        namespace ranges = std::ranges;

        const auto v = {3, 1, -14, 1, 5, 9, -14, 9};

        auto result = ranges::max_element(v.begin(), v.end());
        std::cout << "Max element at pos " << ranges::distance(v.begin(), result) << '\n';

        auto abs_compare = [](int a, int b) { return std::abs(a) < std::abs(b); };
        result = ranges::max_element(v, abs_compare);
        std::cout << "Absolute max element at pos "
                  << ranges::distance(v.begin(), result) << '\n';
    }

Output:

    Max element at pos 5
    Absolute max element at pos 2

### See also

ranges::min_element (C++20) | returns the smallest element in a range (algorithm function object)
ranges::minmax_element (C++20) | returns the smallest and the largest elements in a range (algorithm function object)
ranges::max (C++20) | returns the greater of the given values (algorithm function object)
max_element | returns the largest element in a range (function template)

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